Glue stck torch
This project, developed around 2005, involves constructing a torch using a glue stick, which conveniently accommodates an AA battery within its plastic casing. To create a functional battery holder, contacts for both the positive and negative connections are necessary. The negative contact is achieved by modifying the internal plastic worm gear of the glue stick, creating a hole for a wire to pass through. The positive contact utilizes a metal wire that rests on top of the battery and is secured by a spring, facilitating easy battery replacement. The wire for the positive contact is positioned near the black "knob" at the bottom, allowing it to connect with another wire when the knob is turned, thereby functioning as a switch to control the torch. Initially, two white LEDs were intended as the light source, but they require approximately 3.6V to operate, while an AA battery provides only 1.5V. Consequently, a switching step-up circuit was necessary to convert the varying input voltage from 1.5V down to below 1V (due to battery discharge) into the required 3.6V (or 7.2V for series-connected LEDs). The circuit had to be compact enough to fit within the limited space of the glue stick's black knob. When the base of the transistor is kept at 0V, the output voltage (Vout) equals Vin - 0.7V (the voltage drop across D1), as the inductor behaves like a wire. However, when a square wave is applied to the base, the transistor operates as a switch, alternating between open and closed states. In the closed state, the inductor connects to Vin and ground, causing the current to increase linearly over time. When the switch opens, the inductor generates a voltage spike to maintain the current, which can exceed Vin, is rectified by D1, and smoothed to direct current by C1. Notably, this circuit demonstrates that a useful oscillator can be constructed using just one transistor. The principle underlying this design is Barkhausen's criterion, which states that a circuit can oscillate if it has a closed loop with a unity gain and a phase shift of k360°. In this circuit, the transistor contributes a 180° phase shift, while a transformer provides the additional 180° phase shift required. If the loop gain is exactly one at a specific frequency, a sine wave oscillator would be produced, albeit with potential startup issues. This circuit was intentionally designed with a loop gain exceeding one, which theoretically suggests that the output could diverge to infinity; however, practical limitations such as clamping or saturation occur. The oscillator's output (the collector of Q1) is constrained by a lower bound of zero and an upper bound determined by the load. Even without a load, the upper bound is defined by the transistor's breakdown voltage. The circuit generates a clean square wave after a startup phase, which is suitable for the intended application. The maximum output voltage is intentionally limited to 7.9V, accounting for the 7.2V drop across two series-connected white LEDs and the 0.7V drop across D1. This circuit's advantageous feature is its adaptability to the load voltage (the LEDs) without requiring resistors or additional current-limiting components. It can accommodate one or three LEDs, with the current through the LEDs varying accordingly, while the output current is influenced by multiple factors.
The circuit schematic for this project includes a single transistor oscillator, which is a compact and efficient design. The primary components consist of a transistor (Q1), a transformer for phase shifting, an inductor for energy storage, a diode (D1) for rectification, and a capacitor (C1) for smoothing the output. The inductor is critical in this design, as it stores energy when the transistor is in the closed state and releases it as a voltage spike when the transistor opens. The transformer, which is integral to achieving the necessary phase shift, operates in conjunction with the transistor to maintain oscillation. The circuit's feedback loop ensures that the output remains stable under varying load conditions, allowing for flexibility in LED configuration. This design exemplifies a minimalist approach to circuit design, showcasing the potential of a single transistor to create a functional and adaptable power source for LED applications.This is a rather old project I`ve done around 2005 but was not published on my website until now. The idea of building a torch using a glue stick came to my mind when I realized that an AA battery fits perfectly into the glue stick`s plastic case. To make a complete battery holder there is also the need to make contacts for the positive and negati
ve connections on the battery. The negative contact is made by cutting the plastic worm gear inside the stick, making a hole in it and passing a wire through the hole. The positive contact is made with a metal wire folded on top of the battery and kept in place using a spring.
This makes it easy to replace the battery. The wire of the positive contact ends close to the black "knob" on the bottom, so that when turning the knob it makes contact with another wire, resulting in a switch to turn the torch on and off. I wanted to use two white LEDs as light source for this torch, but this turned out to be a problem because a white LED requires ~3.
6V to operate, while an AA battery is only 1. 5V. So I had to come up with some sort of switching step-up circuit to provide 3. 6V (or 7. 2V if wiring the LEDs in series) from an input voltage that varies from 1. 5V down to less than 1V (because battery voltage decreases as the battery discharges). And the circuit needed to be small enough to fit into the tiny space available into the black knob of the glue stick. If the base of the transistor is kept at 0V Vout is just Vin-0. 7 (the voltage drop of D1) because the inductor acts as a wire. But if a square wave is applied to the base of the transistor, it acts as a switch opening and closing.
When the transistor is closed the inductor is connected to Vin and ground, and the current in it increases linearly with time, while when the switch opens the inductor geneartes a voltage spike to try keeping the current constant. This voltage can be higher than Vin, so it is rectified by D1 and leveled to a direct current by C1. In a time where high-end GPUs reached the score of a billion transistors it is interesting to know that it is possible to build an useful circuit with just one transistor.
That`s right, here`s the schematic of the one-transistor oscillator The trick here is the Barkhausen`s criterion. If a circuit has a closed loop and there is a frequency in the loop gain that has a unity gain and a phase shft of k360 °, then it can oscillate.
In this circuit the transistor accounts for a 180 ° phase shift, and a transformer is used to get the other 180 ° phase shift necessary. Now, if the closed loop gain would be exactly one at some frequency, we would have a sine wave oscillator at that frequency (together with oscillator start-up issues).
In this case the circuit was built on purpose with a loop gain greater than one, and this mathematically speaking would mean that the output would diverge to infinity. In practice clamping (or saturation) occurs. The output of the oscillator (whic is the collector of Q1) has a lower bound of zero by design, and the upper bound depends on the load applied.
Even with no load the bound would be the transistor`s breakdown voltage. To get a (not that much precise) impression of what`s happening, see these three lines of Scilab code: As can be seen, after a start up phase, the circuit generates a rather clean square wave, which is what we need for the task after all. The upper bound of the output voltage in the graph is set on purpose to 7. 9V, because it is 7. 2 + 0. 7, where 7. 2 is the voltage drop of two white LEDs in series, and 0. 7 is D1`s voltage drop. The nice thing of this circuit is that it will adapt to the load voltage, in this case the LEDs, without requiring resistors or other current limiting components.
If you attach one or three LEDs, it will still work, though the current in the LEDs will change. In fact, the last thing to choose is the output current. In this circuit it depends on many 🔗 External reference
The circuit schematic for this project includes a single transistor oscillator, which is a compact and efficient design. The primary components consist of a transistor (Q1), a transformer for phase shifting, an inductor for energy storage, a diode (D1) for rectification, and a capacitor (C1) for smoothing the output. The inductor is critical in this design, as it stores energy when the transistor is in the closed state and releases it as a voltage spike when the transistor opens. The transformer, which is integral to achieving the necessary phase shift, operates in conjunction with the transistor to maintain oscillation. The circuit's feedback loop ensures that the output remains stable under varying load conditions, allowing for flexibility in LED configuration. This design exemplifies a minimalist approach to circuit design, showcasing the potential of a single transistor to create a functional and adaptable power source for LED applications.This is a rather old project I`ve done around 2005 but was not published on my website until now. The idea of building a torch using a glue stick came to my mind when I realized that an AA battery fits perfectly into the glue stick`s plastic case. To make a complete battery holder there is also the need to make contacts for the positive and negati
ve connections on the battery. The negative contact is made by cutting the plastic worm gear inside the stick, making a hole in it and passing a wire through the hole. The positive contact is made with a metal wire folded on top of the battery and kept in place using a spring.
This makes it easy to replace the battery. The wire of the positive contact ends close to the black "knob" on the bottom, so that when turning the knob it makes contact with another wire, resulting in a switch to turn the torch on and off. I wanted to use two white LEDs as light source for this torch, but this turned out to be a problem because a white LED requires ~3.
6V to operate, while an AA battery is only 1. 5V. So I had to come up with some sort of switching step-up circuit to provide 3. 6V (or 7. 2V if wiring the LEDs in series) from an input voltage that varies from 1. 5V down to less than 1V (because battery voltage decreases as the battery discharges). And the circuit needed to be small enough to fit into the tiny space available into the black knob of the glue stick. If the base of the transistor is kept at 0V Vout is just Vin-0. 7 (the voltage drop of D1) because the inductor acts as a wire. But if a square wave is applied to the base of the transistor, it acts as a switch opening and closing.
When the transistor is closed the inductor is connected to Vin and ground, and the current in it increases linearly with time, while when the switch opens the inductor geneartes a voltage spike to try keeping the current constant. This voltage can be higher than Vin, so it is rectified by D1 and leveled to a direct current by C1. In a time where high-end GPUs reached the score of a billion transistors it is interesting to know that it is possible to build an useful circuit with just one transistor.
That`s right, here`s the schematic of the one-transistor oscillator The trick here is the Barkhausen`s criterion. If a circuit has a closed loop and there is a frequency in the loop gain that has a unity gain and a phase shft of k360 °, then it can oscillate.
In this circuit the transistor accounts for a 180 ° phase shift, and a transformer is used to get the other 180 ° phase shift necessary. Now, if the closed loop gain would be exactly one at some frequency, we would have a sine wave oscillator at that frequency (together with oscillator start-up issues).
In this case the circuit was built on purpose with a loop gain greater than one, and this mathematically speaking would mean that the output would diverge to infinity. In practice clamping (or saturation) occurs. The output of the oscillator (whic is the collector of Q1) has a lower bound of zero by design, and the upper bound depends on the load applied.
Even with no load the bound would be the transistor`s breakdown voltage. To get a (not that much precise) impression of what`s happening, see these three lines of Scilab code: As can be seen, after a start up phase, the circuit generates a rather clean square wave, which is what we need for the task after all. The upper bound of the output voltage in the graph is set on purpose to 7. 9V, because it is 7. 2 + 0. 7, where 7. 2 is the voltage drop of two white LEDs in series, and 0. 7 is D1`s voltage drop. The nice thing of this circuit is that it will adapt to the load voltage, in this case the LEDs, without requiring resistors or other current limiting components.
If you attach one or three LEDs, it will still work, though the current in the LEDs will change. In fact, the last thing to choose is the output current. In this circuit it depends on many 🔗 External reference
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